Electroluminescent panels have been used for many years in electrophotographic apparatus to expose a photoconductive member with uniform radiation. For example, they have been used as an interframe erase lamp, a pre-development erase lamp, a pre-cleaning erase lamp, and to control the primary charge placed on the photoconductor.
In such devices the panel is placed across the photoconductor either touching or extremely close to it and the photoconductive member moves past it. The amount of exposure given the photoconductive member is a function of the intensity of the illumination from the electroluminescent panel and the time each point on the photoconductive member is exposed to that illumination. In general, the level of illumination of the electroluminescent panel is constant across the panel. The time is a function of the in-track width of the panel and the speed of the photoconductive member.
Many of the applications mentioned above of the electroluminescent panel involve total discharge of the photoconductive member. In these applications the actual amount of exposure is not critical. When the electroluminescent panel is used between the primary charger and the exposure station in electrophotographic apparatus to control or vary the amount of charge entering the exposure station, the photoconductive member is only partly discharged, and it becomes important that the exposure be uniform across the photoconductor.
The in-track width of an electroluminescent panel is controlled by a mask with an elongated aperture. Conventionally, that mask is one wall of a plastic casing for the panel, with the aperture cut out of the wall. Unfortunately, typical requirements for the mask involve an extremely long thin aperture, for example, 345 mm. cross-track length by 61/2 mm. in-track width. The panel is similarly thin, forcing the mask to have elongated narrow strips of plastic along each side. Although such strips may be connected to other walls of the casing, they have a tendency to bow in use. The bowing widens the aperture in the middle and causes the photoconductive member to receive greater exposure as it moves under it. This reduces the charge in the middle of the image area and adversely affects the electrostatic image produced.